#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <arpa/inet.h>
#include <sys/socket.h>
#define BUF_SIZE 1024
#define OPSZ 4
void error_handling(char* message);
int calculate(int opnum, int opnds[], char op);

int main(int argc, char* argv[]) {
    int serv_sock, clnt_sock;
    char opinfo[BUF_SIZE];
    int result, opnd_cnt, i;
    int recv_cnt, recv_len;
    struct sockaddr_in serv_addr, clnt_addr;
    socklen_t clnt_addr_sz;
    if (argc != 2) {
        printf("Usage: %s <port> \n", argv[0]);
        exit(1);
    }

    serv_sock = socket(PF_INET, SOCK_STREAM, 0);
    if (serv_sock == -1) 
        error_handling("socket() error");
    
    memset(&serv_addr, 0, sizeof(serv_addr));
    serv_addr.sin_family = AF_INET;
    serv_addr.sin_addr.s_addr = htonl(INADDR_ANY);
    serv_addr.sin_port = htons(atoi(argv[1]));

    if (bind(serv_sock, (struct sockaddr*)&serv_addr, sizeof(serv_addr)) == -1)
        error_handling("bind() error");
    if (listen(serv_sock, 5) == -1)
        error_handling("listen() error");

    clnt_addr_sz = sizeof(clnt_addr);
    opnd_cnt = 0;
    clnt_sock = accept(serv_sock, (struct sockaddr*)&clnt_addr, &clnt_addr_sz);
    read(clnt_sock, &opnd_cnt, 1);
    recv_len = 0;
    while (recv_len < (opnd_cnt * OPSZ + 1)) {
        recv_cnt = read(clnt_sock, &opinfo[recv_len], BUF_SIZE - 1);
        recv_len += recv_cnt;
    }
    result = calculate(opnd_cnt, (int*)opinfo, opinfo[recv_len - 1]);
    write(clnt_sock, &result, sizeof(result));
    close(clnt_sock);
    close(serv_sock);
    return 0;
}

int calculate(int opnum, int opnds[], char op) {
    int result = opnds[0], i;
    switch (op)
    {
    case '+':
        for (i = 1; i < opnum; i ++) result += opnds[i];
        break;
    case '-':
        for (i = 1; i < opnum; i ++) result -= opnds[i];
        break;
    case '*':
        for (i = 1; i < opnum; i ++) result *= opnds[i];
        break; 
    }
    return result;
}
void error_handling(char* message) {
    fputs(message, stderr);
    fputc('\n', stderr);
    exit(1);
}